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					<h1>Madison County, Va, 1995 Debris Flow</h1>

					<p>By:</p>
					<p>Michelle Chan, Lizzie Coughlan, Sophie Peet , Joshua Tucker</p>
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				<h2 class="major">Madison, Va, Debris Flow 95</h2>

				<h3>Where and when did this event happen?</h3>
				<p>There were six landslide events, one happened the 19 and 20
					of August 1969 and one happened on June 27, 1995. They were both
					located in western Madison and Greene counties in central Virginia
					in the Blue Ridge physiographic province, this is where the meadow
					run stream is located. This area of the blue ridge has many
					alluvial fans. This event involved the Rapidan River and some of
					its major tributaries, the Robinson, Conway, and South Rivers which
					are the headwaters for the Rappahannock River.</p>

				<h3>What were the geologic setting and the local conditions
					that made this a location where a mass-wasting event of this type
					was likely to happen, and what is the evidence of similar events
					happening in that area in the past?</h3>
				<p>This was a summer day with a lot of moisture content in the
					air, and a high liquid water content in the clouds, but the max
					precipitation for a day like that was around 48mm, so they received
					nearly 17x that in a matter of hours. There was a high pressure
					system coming from the north and a low pressure system coming from
					the south that day. Historical evidence studying the sediment and
					the rocks shows that there was a large volume of mechanical
					weathering during the pleistocene era. Study of the debris fans
					shows evidence of heavy debris flow every 2500 years, so this is
					not a one of a kind event. The slopes were characterized by low
					vegetation and increase frost activity from the Wisconsin
					glaciation, these two things increase the chance and the volume of
					mechanical weathering and solifoliation.</p>
				<p>There have been 5 landslide events. These events were caused
					by severe storms that caused severe erosion.</p>
				<p>As the size of the region increases, so does the probability
					of debris flow activity. In the past, storms that cause debris flow
					have happened at 10-15 year intervals. In landscapes like the
					Piedmont, it is noted that debris flow is rare due to low slope
					gradients and relief, as well as lesser rainfall. Researchers
					proposed that high magnitude events tend to significantly alter
					high relief landscapes (Eaton). However, there is not yet enough
					data to test that hypothesis.</p>
				<h3>What was the proximate cause of the event, i.e. what caused
					the system to cross a physical threshold leading to slope failure -
					most often that turns out to be either a storm event or an extended
					period of above-normal precipitation but it will vary by event?</h3>
				<p>All of these events were caused by severe storm and hurricane
					events. In the 1995 event (The Rapidan Storm), there was an
					accumulation of 775mm (30.5 inches) of rainfall within 16 hours.
					Some key elements that made this storm so harsh were a nearly
					saturated atmospheric column of air 6km above ground, strong
					boundary winds upsloping towards the mountains, light upper level
					winds facilitating small storm motion, and large precipitable water
					values.</p>
				<p>Hurricane Isabel in 2003 with rainfall of up to 27.9 cm in 24
					hours, in the Blue ridge, this would not reach the critical
					threshold which would have resulted in a landslide or debris flow,
					but this events resulted in 5 small landslides.</p>
				<p>Caused by four major storms that triggered debris flows. Two
					storms happened in the Blue Ridge Mountains of Virginia and the
					other two happened in the the Valley and Ridge province of western
					Virginia, and eastern West Virginia (Eaton, 2003).</p>
				<p>On June 27, 1995, a storm hung over the Rapidan River basin
					in Virginia. It was the product of a stalled cold front and a
					westward flowing, moisture laden air moving towards the east
					towards the Blue Ridge Mountains. It was noted that the maximum
					rainfall total equated to 775 mm in 16 hours. This storm triggered
					more than 1000 debris flows and caused massive flooding in the
					area. Later that day, there was another storm that took place over
					the North Fork of the Moormans River. This was located 45 km south
					of the Rapidan River basin. Here, rainfall was measured to be
					anywhere from 279 mm to 635 mm, causing around 200 debris flow
					(Eaton, 2003). The 1995 storm caused 30 inches of rain to fall on
					Madison County in a matter of 16 hours.</p>
				<h3>What was the physical mechanism involved in the slope
					failure (most of them are some form of debris flow but there are
					somewhat different scenarios depending on the case study) and what
					evidence was used to figure out what physical processes were
					involved?</h3>
				<p>There were debris flows as a result of these storms in the
					form of landslides. To determine this researchers were able to
					study the alluvial fans to figure of what kind of materials were
					transported during this event. They were able to determine the
					types of minerals found in these fans, such as silt, sand, gravel,
					cobbles from quartzites, sandstones, and phyllites. Through
					studying the fans they determined there were 1000 slope failures
					which exposed deeply incised early fluvial deposits, stream
					channels, and alluvial fans showing the large transport of debris.</p>
				<p>Researchers studied the trees to determine the time the
					events took place. They were able to find the minimum age of the
					surface the tree was growing on. They can determine this from root
					damage, and radial growth patterns.</p>
				<p>Researchers were also able to analyze stratified slope
					deposits, which are the mineral deposits. They did this using
					radiocarbon dating.</p>
				<p>Stream discharge was very crudely measured but it reported
					that it was 1.4 times the mea discharge.</p>
				<p>Average loss of sediments from the Rapidan River basin caused
					by the major storm amounted to 2.7 cm.</p>
				<p>Debris flow from the storm partially filled the Sugar Hollow
					Reservoir which quickly reduced the holding capacity by 15%,
					leading to 0.9 cm of sediment loss. It is noted that this number is
					the minimum amount of denudation lost since most of the silt and
					clay (materials that make up the upland regolith) may have been
					flushed beyond the reservoir due to the small particle size (Eaton,
					2003).</p>
				<p>In this case alone, it was found that the primary contributor
					to erosion during large floods were the mechanical loads. Almost
					half of long term erosion in this area is a result of debris flow
					activity caused by storms (Eaton, 2003)</p>
				<h3>To the extent that there were serious consequences of this
					event for public safety, could those consequences have been avoided
					or mitigated with better understanding of the hazard?</h3>
				<p>3 fatalities associated with this storm and millions of
					dollars in damages.</p>
				<p>The general population in this area consists of farmers. Due
					to the severity of the storm, many communities were isolated due to
					telephone, electricity, road, and bridge failures. Houses and barns
					were crushed by the debris flow. Trees were carried into streams
					and used as rams against buildings and bridges, increasing the
					destructive power of the storm. In total, there were 8 fatalities
					and damage estimated at over 100 million (USGS Fact Sheet, 159-96).</p>
				<p>In order to avoid or mitigate the same consequences that have
					happened in the past, scientists have studied the storm and its
					effects. For prevention purposes, people who live in the area can
					learn about the land around them, figuring out if debris flows have
					happened in their area could be a good indicator of whether debris
					flows will happen in the future. Storm water drainage should be
					tracked and recorded, it is especially important to note signs of
					land movement (small landslides or tilting trees). Many times, the
					local authorities can educate people about the emergency response
					and evacuation procedures in that area.</p>
				<p>During massive storms, it suggested that people should stay
					awake. Continue to track the weather through the news or radio. It
					is also important to listen for sounds that may indicate debris
					flows like cracking trees or knocking boulders. Usually landslides
					are preceded by a trickle of flowing mud and an increase of
					sediment in nearby bodies of water. If living in an area that is
					susceptible to landslides, evacuate if it is currently safe to do
					so. If there is a second floor, people should evacuate to the
					second floor of the building. If driving, be sure to look out of
					collapsed pavement, mud, rocks, or anything else that could
					indicate debris flow (USGS Fact Sheet, 159-96).</p>
				<h3>6. In what way does this case study resemble the
					description or characterization of similar processes in the
					textbook and in what way does what you were able to learn about the
					event either go beyond or differ from the basic information covered
					in the relevant chapter in the textbook?</h3>
				<p>We learned that large magnitude, infrequent events only
					transport a small percentage of the total annual sediment in large
					lower-gradient river basins (Eaton, 2003). However, for smaller
					river basins, the same large magnitude, infrequent events play a
					big role in the erosion of the landscape. These effects also tend
					to be long term. The rate of erosion in the Appalachians are within
					the US average (interesting because would’ve thought erosion rates
					would be higher). It was also noted that there was a very low
					correlation of denudation with physiography and geology. This may
					be due to a limited data set. However, the highest correlation was
					found between storm rainfall totals and denudation. It was noted
					that the Blue Ridge basins have received more rainfall during
					debris flow events than the Valley and Ridge basins which could be
					the reason why there was greater denudation in the former (Eaton,
					2003).</p>

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				<h2 class="major">Related Events</h2>
				<h3>Hurricane Camille</h3>
				<p>On August 19, 1969, the last of Hurricane Camille crossed the
					Blue RIdge Mountains (Eaton). It was measured that average (mean)
					losses of sediments from three basins amounted to 4.3 cm (due to
					Hurricane Camille). Due to Hurricane Camille, over a period of 7-8
					hours, 711 mm of rain fell during the early morning. This flood
					triggered thousands of debris flows and killed around 125
					people.This was not a densely populated area so that amounted to 1%
					of the regions population (Eaton, 2003).</p>
				<h3>1949</h3>
				<p>Storm as the result of convective storm cells. This storm
					only affected a few mountainous basins. The total amount of
					rainfall produced was 229 mm in western virginia and less than 380
					mm in eastern west virginia. This storm triggered dozens of debris
					slides and flows (Eaton, 2003).</p>
				<h3>1985</h3>
				<p>In November of 1985, storm that took up the most area. Rain
					fell at moderate intensity for a duration of 3 days. The storm was
					said to produce 250 mm of rain and was created by two low pressure
					systems and the end of Hurricane Juan. Initiated thousands of
					debris flow and occured over the same region as the 1949 storm.
					Average erosion rate taken from two different basins equated to 0.2
					cm (Eaton, 2003).</p>

				<h3>Other Notes</h3>
				<p>It was noted in the Eaton paper that the role of high
					magnitude events on geomorphic effectiveness and landscape
					evolution has been underestimated when it comes to the Appalachians
					and other mountainous terrains located in humid-temperate climates.
					Most of the upland channels that was affected by this storm have
					been slow to recover. Specific landforms in the Appalachians like
					debris fans and levees, boulder bars and terraces, wide linear
					alluvial valleys, and single channel floodplains that become
					brainded during massive flooding are due to high magnitude,
					infrequent events (Eaton, 2003)</p>
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				<h2 class="major">Gallery & Fact Sheet</h2>
				<p>Madison County Va</p>
				<span class="image main"><img src="images/MadisonCountyVa.png" alt="" /></span>
				<p><a href="https://commons.wikimedia.org/w/index.php?curid=573569">https://commons.wikimedia.org/w/index.php?curid=573569</a></p>
				<iframe  src="https://pubs.usgs.gov/of/2003/of03-410/shenandoah.pdf" style="position: relative; height:938px ; width: 100%;"
					></iframe>
					<p><a href="https://pubs.usgs.gov/of/2003/of03-410/">USGS</a></p>

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				<p>
					Background image form <a
						href="https://unsplash.com/photos/pTdTkyFiJFY">unsplash.com</a>
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				<p>
					Template For website from <a href="https://html5up.net/dimension">html5.net</a>
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				<p>Map of Madison county By David Benbennick - The maps use data from nationalatlas.gov, specifically countyp020.tar.gz on the Raw Data Download page. The maps also use state outline data from statesp020.tar.gz. 
				The Florida maps use hydrogm020.tar.gz to display Lake Okeechobee., Public Domain, <a href="https://commons.wikimedia.org/w/index.php?curid=573569">https://commons.wikimedia.org/w/index.php?curid=573569</a></p>
				<p>Eaton, L. S., Morgan, B. A., Kochel, R. C., & Howard, A. D.
					(2003). Role of debris flows in long-term landscape denudation in
					the central Appalachians of Virginia. Geology,31(4), 339-342.
					doi:10.1130/0091-7613(2003)0312.0.co;2</p>
			
				<p>Gori, P. L., & Burton, W. C. (1996). Debris-flow hazards in
					the Blue Ridge of Virginia (United States Geological Survey, Ed.).
					Fact Sheet,159-196. doi:10.3133/fs15996</p>

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